Gas separation is important in various industries and can typically be accomplished by flowing a mixture of gases over an adsorbent that preferentially adsorbs a more readily adsorbed component relative to a less readily adsorbed component of the mixture. Gas separation by swing adsorption, such as pressure swing adsorption (PSA), temperature swing adsorption (TSA) and partial pressure swing or displacement purge adsorption (PPSA) is achieved when a first gas component is more readily adsorbed on an adsorbent material compared to other gas components in the gas mixture. In many important swing adsorption applications, described as “equilibrium-controlled” processes, the adsorptive selectivity is primarily based upon differential equilibrium uptake of first and second components. In another important class of swing adsorption applications, described as “kinetic-controlled” processes, the adsorptive selectivity is primarily based upon the differential rates of uptake of the first and second components.
In PSA processes, a target gaseous component is separated from a gas mixture by use of cyclic variations of pressure coordinated with cyclic flows of the gas mixture, component product streams, and/or purge streams contacting a bed comprised of adsorbent material in an adsorber vessel. In the case of TSA or PPSA processes, cyclic variations of temperature and/or partial pressure of the gas components may be coordinated with gas flow through a flow path to perform a separation. The process in any specific PSA application operates at a cyclic frequency characterized by its period, and over a pressure envelope between a first relatively higher pressure and a second relatively lower pressure. Separation by PSA is achieved by coordinating the pressure variations with the flow pattern of the streams, so that at least a first product stream is obtained from the gas mixture which is enriched in at least a second component in the gas mixture (owing to preferential adsorptive uptake of a first component in the adsorbent material) when flowing through the adsorbent material, while at least a second product stream is obtained which is enriched in the first component when desorbed by the adsorbent material during subsequent process steps. In order to achieve separation performance objectives (i.e., product gas purity, recovery and productivity), process parameters and operating conditions are designed to achieve a sufficiently high adsorptive selectivity of at least the first and second components in the adsorbent material, at the cyclic frequency and within the pressure envelope.
In kinetic-controlled adsorption processes, separation over a given adsorbent material may be achieved between a first component, which adsorbs and typically also desorbs relatively more rapidly at a particular cycle frequency, and a second component which adsorbs and typically desorbs relatively less rapidly at the cycle frequency. Such adsorption and desorption are typically caused by cyclic pressure variation, whereas in the case of TSA, PPSA and hybrid processes, adsorption and desorption may be caused by cyclic variations in temperature, partial pressure, or combinations of pressure, temperature and partial pressure, respectively.
In the case of PSA, kinetic-controlled selectivity may be determined primarily by micropore mass transfer resistance (e.g., diffusion within adsorbent particles or crystals) and/or by surface resistance (e.g., narrowed micropore entrances). For successful operation of the process, a relatively and usefully large working uptake (e.g., the amount adsorbed and desorbed during each cycle) of the first component compared to a relatively small working uptake of the second component is preferably achieved. Hence, a kinetic-controlled PSA process can be operated at a suitable cyclic frequency, balancing between and avoiding excessively high frequencies where the first component cannot achieve a useful working uptake, and excessively low frequencies where both components approach equilibrium adsorption values.
Gas separation processes are generally energy intensive and thus there are important opportunities for the introduction of more energy efficient systems based on membranes and advanced sorbent materials. In addition, CO2 capture is a major area of current interest due to the threat of global warming. In the energy industry, separation of CO2 from CH4 is important and requires an efficient, environmentally benign solution. However, each potential application is generally different in composition, temperature, pressure, proximity to land, etc. and each application of the technology typically requires a different separation strategy and system design and/or configuration. In the current art, selection of adsorbent materials useful for a particular application are typically discovered empirically by testing, or by trial and error, and thus are difficult if not near impossible to pre-determine structured adsorbent compositions that are optimized for a particular separation or a particular set of separation conditions. The present invention provides a method for materials optimization and reduction of testing and selection, and the potential for producing a slate of new adsorbent materials specifically designed for a given gas separation application.